Multiple quantum wells are semiconductor structures comprised of alternating thin layers of two different semiconductor materials and, in particular, of semiconductor materiais having differing bandgaps. Typically, layer thicknesses are of the order of 100 .ANG. and a typical structure might comprise 100 such layers, resulting in a total thickness of about 1 micrometer. Multiple quantum well structures are typically produced using molecular beam epitaxy or metal-organic chemical vapor deposition sometimes known as organometallic vapor phase epitaxy. Multiple quantum well structures have been used successfully in many different optical devices, such as optical modulators.
An example of a multiple quantum well structure may be found in the co-pending application of Mitra Dutta entitled "Optical Modulator Based On .GAMMA.-X Valley Mixing in GaAs-AlAs", Ser. No. 07/765,215, filed Sep. 20, 1991. An example of an optical modulator employing the multiple quantum well structure of the foregoing application may be found in the co-pending application of Mitra Dutta and Hongen Shen entitled "All Optical Multiple Quantum Well Optical Modulator," filed concurrently herewith. Other examples of both electrically controlled and optically controlled multiple quantum well devices can be found in an article by D. A. B. Miller, "Optoelectronic Applications of Quantum Wells,"Optics Photonics, Vol. 1, No. 2, page 7, February 1990.
Although optical multiple quantum well modulators have a number of advantages, the present invention is based on the recognition that significant other advantages can be achieved by multiple quantum well modulators based on phonon stimulation and emission, rather than photon stimulation and emission.
The existence of interface longitudinal-optical (LO) phonons in quantum wells is well known. See, for example, R. Fuchs et al, Phys. Rev. 140, A2076 (1965); K. Mori et al, Phys. Rev. B40, 6175 (1989); G. Fasol et al, Phys. Rev. B38, 6056 (1988); L. P. Fu et al, Phys. Rev. B. 46, 796 (1992).
In addition to interface LO phonons, quantum wells also contain sinusoidal or confined phonons. The general characteristics of both confined and interface LO phonons in quantum wells are described in "Electron Phonon Interaction in a Dielectric Slab: Effect of the Electronic Polarizability," James H. Licari et al, Phys. Rev. 15, 2254 (1977). Further background on interface LO phonons and confined LO phonons in semiconductors may be found in the following: Michael A. Stroscio et al, Appl. Phys. Lett., 59, 1093 (1991); K. W. Kim et al, J. Appl. Phys., 70, 319 (1991); D. S. Kim et al, Phys. Rev. Lett., 68, 1002 (1992); N. Mori et al, Semicond. Sci Technol., 7, B83 (1992); and P. G. Klemens, Phys. Rev. 148,845 (1966).